Suppression of the immune system, particularly the humoral immune system, is beneficial in organ transplantation and treatment of autoimmune disorders. Organ transplantation has emerged as a preferred method of treatment for many forms of life-threatening diseases that involve organ damage. However, transplantation rejection may occur when an organism receiving transplanted cells or tissue mounts an undesired immune response to that tissue. Transplant rejection may be minimized by tissue-type matching, but even matched tissue can be rejected by the donor. Thus, immunosuppressive therapies are now used for virtually all cases of tissue transplantation.
Improved results in clinical transplantation have been achieved primarily through the development of increasingly potent non-specific immunosuppressive drugs to inhibit rejection responses. While short-term results have improved, long-term outcomes remain inadequate. Life-long immunosuppressive agents may be required to combat chronic rejection of the transplanted organ, and the use of these agents dramatically increases the risks of cardiovascular disease, infections, and malignancies.
One potential target for reducing transplantation rejection is the CD40/CD154 interaction. CD40 is expressed primarily on the surface of B lymphocytes and other antigen-presenting cells (APCs) such as dendritic cells and macrophages. CD154 is expressed primarily on the surface of T cells. The interaction between these two proteins is associated with B cell activation, which triggers cytokine expression as well as expression of cell surface markers including CD23, CD80, and CD86, Kehry M. R., CD40-mediated signaling in B cells. Balancing cell survival, growth, and death, J. Immunol. 1996; 156: 2345-2348. Blockade of this interaction using anti-CD154 antibodies has been shown to reduce or eliminate rejection of transplanted tissues in non-human primates.
For any type of immunosuppression (e.g., in a transplantation procedure), a balance between efficacy and toxicity is a key factor for its clinical acceptance. Thus, there is a need for therapies that specifically target the immunological pathways involved in, for example, transplant rejection and autoimmune disorders.